In the communication systems, computers, or servers, the backplane is an important component providing some functions, such as signal interconnection channels, power supply, or guidance and physical support, for various circuit boards. The backplane typically includes multilayer PCB, signal/power connectors, and guiding mechanism, etc. The multilayer PCB includes multiple layers of integral or bulk copper sheets having certain thickness and functioning as power supply and grounding reference, printed copper wires for providing interconnection channels for signals between the circuit boards, and insulation dielectric.
Generally the backplane is passive. That is to say, there is no active element on the backplane, such as various ICs (integrated circuits). Referring to FIG. 1, the power supply for the backplane 11 is provided by a power supply module 16 in the frame 12. The backplane 11 is connected to the power supply module 16 via a power supply connector 15, and the backplane 11 is connected to circuit boards 13 via a power supply connector 14, so that various ICs arranged on the circuit boards 13 are supplied with power. FIG. 2 is a schematic view showing the interconnection relationship between the backplane 11 and the circuit boards 13 via connectors 20, which are formed from the power supply connectors 14 and 15.
With the development of data broadband, digital television and VOD (Video On Demand) services, requirement for system bandwidth is becoming higher, and capacity of the system is becoming larger. Therefore, requirement for supplying high-power current to the backplane is becoming urgent. To achieve this object, it is attained generally in the conventional backplane by adding several layers of integral (or partial) copper sheets in the multilayer circuit boards. However, general high density backplane includes 20 to 30 layers, and the larger the layer number is, the higher the producing cost of the backplanes is. Further, the relationship between the cost increment and the layer number of the backplane is not linear. Rather, the rate of the cost increment is greater than that of the layer number increment. It is obvious that the producing cost of the backplane will be increased by increasing the layer number of the backplane. Another solution is to lay copper partially on the signal plane or to supply power to the divided areas of the ground plane. This solution decreases the wiring space and increases the wiring difficulty, as well as may further generate interfering signals caused by the power supply noise.
To solve the above problems, separated element, such as busbar, located outside of the backplane can be designed to provide large current. Typical busbar serves as a power supplying and grounding system, and includes multiple layers of copper conductors with insulation dielectric therebetween. The busbar is widely applied to the cabinet of a system.
Now the above technology is applied to the backplane system. The busbar also includes multiple layers of conductors. However, the difference lies in that some needle type base pins, which are designed to be contacted with conductors and can be mounted on the backplanes by press-fitted process, are provided at a distance on the busbar. This busbar is mounted on the backplane by press-fitted process. The press-fitted base pins are closely contacted with the conductors in large areas. Positional arrangement of the base pins can be customized, depending on requirements of the users. The extra base pins can be removed by applying external force. The press-fitted busbar is shown in FIGS. 3, 4A, and 4B.
1. When applying the busbar in the prior art to the backplane, due to the large size of the backplane, generally a long press-fitted busbar is used to extend through the whole backplane, which may cause the following problems:
(A) Maintenance is inconvenient. Because the long busbar is mounted in a press-fitted manner, the press-fitted base pins are required to be closely contacted with the metallized holes in the backplane, which often causes the base pins to be embedded into the metal of the metallized holes. It is quite difficult to remove this kind of busbar out of the metallized holes.
(B) The mounting holes in the backplanes for mounting the busbar in a press-fitted manner need to be processed in high positional precision; otherwise, there will be accumulative error, which may cause the press-fitted busbar not to be mounted on the backplane correctly. However, the higher the processing precision is, the higher the producing cost of the backplane is.
2. If short press-fitted busbars are used to supply power for the whole backplane, the busbars have to be connected with each other in a certain manner, which increases the complexity of mounting the busbars and degrades the system reliability.
As described above, the above two kinds of press-fitted busbars backplane may also cause the deformation of the backplane, in turn cause stress concentration in the backplane and degrade the long-term reliability of the backplane. Because the backplane for different applications may be made of different materials usually having different thermal expansion coefficients, the material for the busbar may have a different thermal expansion coefficient from that of the backplane. The difference of the thermal expansion coefficient causes the deformation of the backplane, causes stress concentration in the backplane, and degrades the reliability of the backplane.